1. Field of the Invention
The present invention relates to a resin diamond blade and a silicon base optical waveguide manufacturing method using the blade.
2. Description of the Related Art
An optical device using an optical waveguide is becoming increasingly necessary with the evolution of optical communication, and the development of optical components such as an optical brancher/coupler, optical multiplexer/demultiplexer, optical modulator, optical switch, and optical wavelength converter is accordingly becoming important. Typical examples of the optical waveguide well known in the art include an optical waveguide formed by diffusing Ti in a single-crystal substrate of LiNbO3, an optical waveguide formed by depositing SiO2 on a silicon substrate, and a polymer optical waveguide. A light incidence end face and a light emergence end face of the optical waveguide correspond to portions for optical coupling of lightwaves propagating in the optical waveguide and lightwaves propagating outside of the optical waveguide. Accordingly, the finished condition of each end face has an important effect on optical loss in the whole of the optical waveguide device.
Each end face of the optical waveguide is conventionally formed by various techniques such as polishing, cleaving, and cutting. The formation of the end face by polishing is superior both in surface roughness of a finished surface and in generation rate of chipping, and this technique is applied to a LiNbO3 optical waveguide and a so-called silicon base optical waveguide formed by depositing SiO2 on a silicon substrate. However, much time is required for polishing, causing a reduction in throughput and an increase in working cost. The formation of the end face by cleaving is applied to a semiconductor optical waveguide of GaAs, for example, and this technique has an advantage that the end face can be quickly obtained with smoothness at a crystal lattice level. However, since this technique is a method utilizing the anisotropy of crystal, the application of this method is limited to a high-cleavage orientation of a high-cleavage material, and this method cannot be applied to a low-cleavage material.
To the contrary, the formation of the end face by abrasive cutting using a diamond blade or the like is applicable also to a low-cleavage material. Moreover, this technique is superior in throughput and working cost because the end face can be formed faster than polishing. Accordingly, this abrasive cutting method has recently been examined as a method for forming the end faces of various optical waveguides. For example, Japanese Patent Laid-open No. Hei 8-68913 discloses a technique of simultaneously performing dicing of a silicon wafer and polishing of the end face of a silicon base optical waveguide by using a resin bonded diamond blade for cutting the optical-waveguide. According to this method described in the above publication, the silicon wafer having the optical waveguide is mounted on a bonded structure, and the resin bonded diamond blade is rotated at a high speed (18,000-35,000 rpm) to cut the silicon wafer being fed at an appropriate speed, thereby simultaneously performing dicing of the silicon wafer and polishing of the end face of the optical waveguide.
The optical waveguide manufacturing method described in the above publication has been followed by the present inventor. As the result, it has been found that the smoothness of the end face of the optical waveguide is insufficient and it cannot be put to practical use unless additional polishing is performed. That is, the end face of the optical waveguide must have a surface roughness (smoothness) of xcex/4 or less where xcex is the wavelength of light for use, so as to sufficiently suppress optical loss in the whole of the optical waveguide device. However, such a smooth end face cannot be obtained by the method described in the above publication, according to the test made by the present inventor.
It is therefore an object of the present invention to provide a silicon base optical waveguide manufacturing method which can form a satisfactory end face of each optical waveguide.
It is another object of the present invention to provide a resin diamond blade which can perform polishing of the end face of each optical waveguide simultaneously with dicing of a silicon wafer.
In accordance with an aspect of the present invention, there is provided a silicon base optical waveguide manufacturing method comprising the steps of performing first-stage dicing of a silicon wafer having a silicon substrate and a plurality of optical waveguides formed on the silicon substrate to form a cut groove by using a first resin diamond blade having a thickness t1; and performing second-stage dicing of the silicon wafer along the cut groove to polish an end face of each of the optical waveguides by using a second resin diamond-blade having a thickness t2 greater than the thickness t1. The second resin diamond blade includes diamond abrasive grains having a grain diameter of 2 xcexcm or less. The relation between the thickness t1 and the thickness t2 is set to t1+0.01 mmxe2x89xa6e t2xe2x89xa6t1+0.05 mm.
Preferably, the second resin diamond blade further includes-cerium oxide abrasive grains having an average grain diameter of 0.1 to 5.0 xcexcm and a purity of 35 to 95 wt %. More preferably, the total content of the diamond abrasive grains and the cerium oxide abrasive grains with respect to the volume of the second resin diamond blade is 20 to 40 vol %. Further the content of the cerium oxide abrasive grains with respect to the total volume of the diamond abrasive grains and the cerium oxide abrasive grains is 35 to 70 vol %. Further, the rotational speed of the first and second resin diamond blades is 10,000 to 30,000 rpm, and the depth of cut per stroke is 0.02 to 1.5 mm. More preferably, the feed speed of the silicon wafer is 0.1 to 1.5 mm/sec in cutting the optical waveguides and 0.1 to 5.0 mm/sec in cutting the silicon substrate.
In accordance with another aspect of the present invention, there is provided a silicon base optical waveguide manufacturing method comprising the steps of bonding a first silicon wafer having a plurality of optical waveguides on a second silicon wafer; performing first-stage dicing of the first and second silicon wafers to form a first cut groove by using a first resin diamond blade having a thickness t1; and performing second-stage dicing of the first and second-silicon wafers along the first cut groove to form a second cut groove shallower than the first cut groove by using a second resin diamond blade having a thickness t2 greater than the thickness t1. The second resin diamond blade includes diamond abrasive grains having a grain diameter of 2 xcexcm or less.
Preferably, the second resin diamond blade further includes cerium oxide abrasive grains having an average grain diameter of 0.1 to 5.0 xcexcm and a purity of 35 to 95 wt %.
In accordance with a further aspect of the present invention, there is provided a resin diamond blade comprising diamond abrasive grains having a grain diameter of 2 xcexcm or less; cerium oxide abrasive grains having an average grain diameter of 0.1 to 5.0 xcexcm and a purity of 35 to 95 wt %; and a bonding resin for bonding the diamond abrasive grains and the cerium oxide abrasive grains. The total content of the diamond abrasive grains and the cerium oxide abrasive grains with respect to the volume of the resin diamond blade is 20 to 40 vol %; the content of the cerium oxide abrasive grains with respect to the total volume of the diamond abrasive grains and the cerium oxide abrasive grains being 35 to 70 vol %.
Preferably, the cerium oxide abrasive grains have an average grain diameter of about 3 xcexcm and a purity of about 60 wt %. Further, the total content of the diamond abrasive grains and the cerium oxide abrasive grains with respect to the volume of the resin diamond blade is about 25 vol %. The content of the cerium oxide abrasive grains with respect to the total volume of the diamond abrasive grains and the cerium oxide abrasive grains is about 50 vol %.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.